1. FIELD OF THE INVENTION
The present invention relates to a process for producing difluorohaloacetyl fluoride (XCF.sub.2 COF:X=1 or Br) which is useful as an intermediate for various fluorine-containing compounds or a compound having special characteristics. For example, difluorohaloacetyl fluoride can be converted into .omega.-haloperfluorocarbon vinyl ether an useful intermediate for thermosetting fluorinated resins, first by adding hexafluoropropylene oxide and then pyrolyzing the resulting adduct. Difluorohaloacetyl fluoride can also be converted into perfluorosuccinyl fluoride by a coupling reaction accomplished by dehalogenation. The resulting perfluorosuccinyl fluoride reacts to give perfluorodicarboxylic acid derivatives by a reaction with a neucleophilic reagent. The derivatives serve to be useful intermediate for fluorine-containing condensation polymers such as polyamides and polyesters having excellent thermal resistance and chemical stability. The difluorohaloacetyl fluorides also serve as a starting material for perfluoro (3-oxa-4-pentenoyl fluoride) or oxalyl fluoride, both of which are useful as intermediates for various fluorine-containing compounds.
DESCRIPTION OF THE PRIOR ART
The only known process for producing difluoroiodoacetyl fluoride is to react tetrafluoroethylene oxide with anhydrous lithium iodide in acetic anhydride. (Japanese Examined Patent Publication No. 8205/1970). However, in the known process, it is necessary to use tetrafluoroethylene oxide which is difficult to produce because of its high potential of explosion and low production yield. Moreover, in this process the yield of difluoroiodoacetyl fluoride based on tetrafluoroethylene oxide is at maximum 40%. Thus, it is not satisfactory for an industrial operation.
On the other hand, as regards to a process for producing difluorobromoacetyl fluoride the preparation of difluorobromoacetate has been known by first heating a mixture of 1,2-dibromochlorotrifluoroethane and fuming sulfuric acid having 40% sulfur trioxide content in the presence of mercury oxide followed by the reaction of the resulting gas with an alcohol. (Tetrahedron. 33, 1445 (1977)). However, when said process is employed for the production of difluorobromoacetyl fluoride, a special purification is required for separating difluorobromoacetyl fluoride from difluorobromoacetyl chloride which is not easily separated from difluorobromoacetyl fluoride since a large amount of difluorobromoacetyl chloride is included in the resulting gas. Moreover, mercury oxide which is included in the reaction system is highly toxic and accordingly, a special treatment is required. Therefore, the process is not satisfactory for an industrial operation.
It has been also proposed to produce difluoroacetyl fluorides by an oxidation of 1-bromo-2-iodo-tetrafluoroethane with an oxidizing acid or by a bromination of difluoroiodoacetyl fluoride. These processes require several reaction steps for producing the starting materials to result in multi-step reactions in total. Therefore, these processes are not satisfactory for an industrial operation.